Project Summary The assessment of radiation organ absorbed dose to patients plays a critical role in both the development and clinical use of radiopharmaceuticals for both diagnostic imaging (cancer/disease detection) and radiation therapy (cancer treatment). Dosimetry also provides the basis of imaging/treatment optimization, and its accessibility and maturation will help define personalized medicine as applied to medical imaging and nuclear therapies in the coming decades. A variety of software codes exist for patient dosimetry in nuclear medicine, but they tend to reside within two extremes of functionality. At one end are more simplistic NM dosimetry tools that merge animal- derived or personalized biodistribution data with standard (population-averaged) models, a technique that has proved valuable historically but has seen minimal technological advancement. At the other end are complex NM dosimetry codes that import patient-specific CT/PET/SPECT images and allow for accurate, but computationally intensive, Monte Carlo simulation-based dosimetry. The issue with these higher-end codes is that they are much more nuanced, resource intensive, and tend to only reside within research-based medical institutions with expert support staff. In this Biomedical Research Partnership between MSK and UF, a new generation of nuclear medicine patient dosimetry code will be developed and released at no cost to the imaging and clinical community. The code ? MIRDcalc ? is built upon the universally available Microsoft Excel platform and can be used with an easy interactive interface or automated DOS command line. The database powering MIRDcalc stores all necessary information for implementing biodistribution-to-dosimetry calculations using the MIRD schema. The current generation of MIRDcalc thus will not include acquisition and derivation of the input time-activity data, which is beyond the scope of the current application, but will be incorporated into future versions of this code. It includes radionuclide S values for 333 radioisotopes, associated with 12 modern ICRP reference phantoms each with 58 source organs and 44 target organs and is readily expandable to accommodate additional isotopes and phantoms. The MIRDcalc software will be a free tool providing dosimetry that meets current standards, and a platform for further innovations as well as a central framework for supporting a dosimetry user community. Our planned innovations address issues of personalization, uncertainty calculation, documentation, and other key considerations. Of note, and a key feature of this partnership, is the addition of CT organ dosimetry to MIRDcalc, which presently does not exist in any current nuclear medicine software code despite the universal adoption of combination PET-CT and the ever-increasing penetration of SPECT-CT scanners in diagnostic radiology and nuclear medicine.